Easy, stop all of your strikes before they make contact with your opponent. It's a good introduction to combat for beginners who might feel intimidated by the prospect of actually being hit. They can work on distance, timing, agnle and all of that good stuff. Additionally, you might want to have them attack the space directly in front of their opponent instead of stopping the attack before it hits, this is good for those students that haven't developed enough control.

If you have children in your classes, no contact sparring is probably a good idea.